6,792 research outputs found
Half-Saturation Constants in Functional Responses
Our aim is to provide an overview of half-saturation constants reported in
literature and to explore their consistency with body size. In many ecological
models, intake of nutrients by plants and consumption of food by animals is
considered to be a hyperbolic function of the nutrient concentration and the
food density, respectively. However, data on the concentration (or density) at
which half of the maximum intake rate is reached are scarce, limiting the
applicability of the computational models. The meta-analysis was conducted on
literature published worldwide. Most studies focused on algae and
invertebrates, whereas some included fish, birds and mammals. The
half-saturation constants obtained were linked to body size using ordinary
regression analysis. The observed trends were compared to those noted in
reviews on other density parameters. Half-saturation constants for different
clades range within one or two orders of magnitude. Although these constants
are inherently variable, exploring allometric relationships across different
taxa helps to improve consistent parameterization of ecological models.Comment: 6 pages, 4 figures, 1 tabl
Universality of Univariate Mixed Fractions in Divisive Meadows
Univariate fractions can be transformed to mixed fractions in the equational
theory of meadows of characteristic zero.Comment: 12 page
C1− Continuous crack propagation for mixed-mode fracture problems
In this work a C1− continuous crack propagation algorithm is proposed to improve the numerical simulation of localized deformation patterns, using higher order elements. The algorithm is applied for a standard smeared crack model and is validated by a mixed-mode fracture problem. From the results a reduction of mesh-induced directional bias is observed
Evaluation of n-alkanes and their carbon isotope enrichments (d13C) as diet composition markers
Plant cuticular n-alkanes have been successfully used as markers to estimate diet composition and intake of grazing herbivores. However, additional markers may be required under grazing conditions in botanically diverse vegetation. This study was conducted to describe the n-alkane profiles and the carbon isotope enrichment of n-alkanes of common plant species from the Mid Rift Valley rangelands of Ethiopia, and evaluate their potential use as nutritional markers. A total of 23 plant species were collected and analysed for long-chain n-alkanes ranging from heptacosane to hexatriacontane (C27 to C36), as well as their carbon isotopic ratio (13C/12C). The analysis was conducted by gas chromatography/combustion isotope ratio mass spectrometry following saponification, extraction and purification. The isotopic composition of the n-alkanes is reported in the delta notation (d13C) relative to the Vienna Pee Dee Belemnite standard. The dominant n-alkanes in the species were C31 (mean ± s.d., 283 ± 246 mg/kg dry matter) and C33 (149 ± 98 mg/kg dry matter). The carbon isotopic enrichment of the n-alkanes ranged from -19.37‰ to -37.40‰. Principal component analysis was used to examine interspecies differences based on n-alkane profiles and the carbon isotopic enrichments of individual n-alkanes. Large variability among the pasture species was observed. The first three principal components explained most of the interspecies variances. Comparison of the principal component scores using orthogonal procrustes rotation indicated that about 0.84 of the interspecies variances explained by the two types of data sets were independent of each other, suggesting that the use of a combination of the two markers can improve diet composition estimations. It was concluded that, while the n-alkane profile of the pasture species remains a useful marker for use in the study region, the d13C values of n-alkanes can provide additional information in discriminating diet components of grazing animal
Analyzing {\gamma}-rays of the Galactic Center with Deep Learning
We present a new method to interpret the -ray data of our inner
Galaxy as measured by the Fermi Large Area Telescope (Fermi LAT). We train and
test convolutional neural networks with simulated Fermi-LAT images based on
models tuned to real data. We use this method to investigate the origin of an
excess emission of GeV -rays seen in previous studies. Interpretations
of this excess include rays created by the annihilation of dark matter
particles and rays originating from a collection of unresolved point
sources, such as millisecond pulsars. Our new method allows precise
measurements of the contribution and properties of an unresolved population of
-ray point sources in the interstellar diffuse emission model.Comment: 24 pages, 11 figure
An algorithm for computing a standard form for second-order linear q-difference equations
In this article an algorithm is presented for computing a standard form for second order linear q-difference equations. This standard form is useful for determining the q-difference Galois group and the set of Liouvillian solutions of a given equation. (C) 1997 Elsevier Science B.V.</p
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